Re. #3: I also find that once I derail I consider it to be a “no-rules” day for the rest of the day. On most goals, though, I’m happy to have it that way, but I can see how it incentivizes a bad-habit binge. I like your solution for this kind of goal (though, I wouldn’t want to actually have it that way for any of mine, I don’t think, as I want my data to be relatively reflective of what was done when, and I do want to be able to at least partially put it out of my mind if I’m going to derail).
I wonder if that’s something that, at least for me, could be fixed with an adjustment to fine print. Like perhaps having some kind of “absolute maximum” even on derail days (that is well above the derail amount for that day). If I hit that "absolute maximum, I have to force a derail on the second day, at the new, higher pledge (and then correct the data afterwards). That way I could still kind of cut loose a little if I’m paying for a derail anyway, but I could also have some kind of upper limit when it comes to just how loose.